Computing power and acceptance of digital transmissions are being designed into a wide range of business and consumer devices. For example, certain player devices, e.g. analog television, may be transformed into a user interface for Internet access. Central to digital broadcasting is a broadcast system, such as a set-top box, that receives and processes signals to enable a player device. A broadcast processing system may receive content from a digital transmitter through a variety of sources, such as local video, cable and satellite channels. The digital transmitter prepares content for sending to the recipient broadcast system.
The digital transmitter creates a continuous bit stream, i.e. transport stream, of audio, video and/or associated data for multiple channels. FIG. 1 depicts a common process for preparing a transport stream that may be performed by a digital transmitter. Audio and video data are received 2 and separately encoded to form respectively audio and video elementary streams 4. Current digital broadcasting environments employ the MPEG-2 (Motion Picture Experts Group 2, ISO (International Standards Organization) Standards 13818, Parts 1, 2, and 3 (November 1994)) file format as the typical compression scheme, but future technology may involve other compression formats.
The streams are formed into packets 6, each of which has a packet header followed by data. A multiplexer combines the elementary stream packets from various encoders together with any security and associated data, e.g. program specific information (PSI), into digital transport stream packets 8. The resulting transport stream is a multiplex of data from numerous channels with a header of information required by a decoder to decompress the packet structures and information indicative of the type of payload in the packet.
The PSI is associated data that is useful or necessary for the ultimate de-multiplexing of a transport stream, i.e. separating the transport stream components, and for the successful regeneration of programs. One type of PSI is a program association table (PAT) that specifies information to translate broadcast codes into the appropriate channel number. The PAT also provides correspondence between program number, i.e. identifier associated with a program, and each packet in a transport stream that carries a program definition. A program definition is a mapping between a program number and the elementary streams that comprise it. A program map table (PMT) is also a PSI that provides for management of all of the PSI tables and carries all of the program definitions for a transport stream. The PMT specifies which elementary streams are associated to form each program by referencing packet identifiers (PID's) for each program number. Another PSI, a conditional access table (CAT), provides encryption keys for the packets that the receiving broadcast system is authorized to play. Encryption for conditional access to programs may be encoded in elementary streams of a transport stream. A network information table (NIT) is an optional PSI for private and predefined content.
The transport stream is sent by the digital transmitter 10 and received by a broadcast processing system, e.g. set-top box. Some sophisticated processing systems permit storing of recorded television broadcasts. However, in general, storing of broadcast data is problematic because it consumes an enormous amount of space in storage.
Processing systems that retain channel data for later playing require the complete transport stream be stored in multiplex form. Thus, not only is data that is relevant to a desired channel kept, but also unwanted data for other channels that are in the multiplexed transport channel are stored. This extra data pointlessly consumes space that is bettered suited for the data that is in fact used for a channel of interest.
The large volumes of stored data in these systems result in a higher bit rate for the system. An exemplary transport stream carries all data for 10 to 12 channels and just one frame of video may result in 3000 to 4000 packets. Thus, these systems store at least ten times the required volume where only a single channel data is wanted. Furthermore, the transport stream is typically pushed into storage at the same high rate in which it enters into the broadcast system, e.g. 45 mbps. The high bit rate tends to cause greater wear on the drive. Moreover, the high capacity drives that are required to handle the heavy load are usually expensive.
In general, the shortcomings of the currently available methods for storing data are inadequate for playing select channel data, at a later time. In particular, previous methods require storing of more data than is required for play.